1. Field of the Invention
The invention relates to compatible mixtures (polymer blends) of a polymer containing cyclopentyl (meth)acrylate as a monomer and a polymer containing styrene, as a monomer.
2. Discussion of the Background
As a rule, different polymer species are incompatible i.e. they do not form a homogeneous phase except at very low concentrations of one species. A homogeneous phase is characterized by complete miscibility of the components.
Certain exceptions to this rule have become increasingly important, particularly among persons concerned with the theoretical aspects of the phenomenon. Completely compatible mixtures of polymers display complete solubility (miscibility) in all mixture ratios.
A comprehensive discussion of compatible polymer systems is found in, e.g., Paul, D.R., et al., 1978, Polymer & Engineering Science, 18, 16:1225-34; 1980, J. Macromol. Sci. Rev. Macromol. Chem. C, 18, 1:109-168.
To demonstrate miscibility, the glass temperature Tg is often employed, or the so-called "optical method" (clarity of a film cast from a homogeneous solution of the polymer mixture) is employed (see Brandrup-Immergut, "Polymer Handbook", 2nd Ed., II:211-213). Another test for the miscibility of essentially different polymers is the occurrence of a lower critical solution temperature (LCST) (see DE-A 34 36 476.5 and DE-A 34 36 477.3). The occurrence of an LCST is based on the process wherein, when a previously clear homogeneous polymer mixture is heated, it separates into phases and becomes cloudy to opaque. Accordingly to the literature, this sequence of events represents unambiguous proof that the original polymer mixture was comprised of a single homogeneous phase in equilibrium.
Recent results on polymer blends and their possible applications are reported in Robeson, L.M., Polym. Engineering & Science, 24, 8:587-597. Copolymers of styrene and maleic anhydride, and of styrene and acrylonitrile, are compatible with polymethyl methacrylate (PMMA) (DE-A 20 24 940). The improved application properties of molding compounds of this type are pointed out as important. Also, copolymers of styrene and monomers which contain hydroxyl groups and are favorable to formation of hydrogen bonds are compatible with polymethacrylates at certain ratios; e.g., copolymers of styrene and p-(2-hydroxyhexafluoroisopropyl)styrene (Min, B.Y. and Pearce, E.M., 1981, Organic Coatings and Plastics Chemistry, 45, 58-64), or copolymers of styrene and allyl alcohol (Cangelose, F., and Shaw, M.T., 1983, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.), 24, 258-259).
Polystyrene itself and other styrene-containing polymers have been found to be incompatible with PMMA. Thus, Shaw, M.T., and Somani, R.H., 1984, Adv. Chem. Ser., 206 (Polym. Blends Compos. Multiphase Syst.), 33-42 (CA 101:73417e) report a miscibility of only 3.4 ppm of PMMA of molecular weight (m.w.) 160,000 with polystyrene, and only 7.5 ppm of PMMA of m.w. 75,000 with polystyrene. Even very low molecular weight polystyrene is largely incompatible with PMMA. Thus, a mixture of 20% of an extremely low molecular weight styrene oligomer (m.w. 3,100) no longer yields a clear product. With a still very low molecular weight polystyrene (m.w. 9,600), a solution of only 5% in PMMA is no longer transparent but only translucent (Parent, R.R., and Tompson, E.V., 1978, Journal of Polymer Science, Polymer Physics Edition, (Vol. 16, 1829-1847).
Other polymethacrylates and polyacrylates are similarly minimally miscible with polystyrene to form transparent plastics. Such is true of, e.g., polyethyl acrylate (PEA), polybutyl methaorylate, polyisobutyl methacrylate, polyneopentyl methacrylate, polyhexyl methacrylate, and numerous others. (See also Somani, R.H., and Shaw, M.T., 1981, Macromolecules, 14:1549-1554.) On the other hand, mixtures comprised of polymers of cyclohexyl (meth)acrylate and styrene have been found to be compatible (see EP-A-0 268 040).
Thus, polystyrene is compatible with copolymers of methyl methacrylate and/or ethyl methacrylate and alkyl methacrylates with 3-24 carbon atoms in the alkyl group, if the copolymers are comprised of units of ethyl methacrylate and/or methyl methacrylate in the amount of 30-90 wt. % and the C.sub.3 -C.sub.24 alkyl methacrylates in the amount of 70-10 wt. % (DE-OS 37 30 025.3). Homopolymers such as PMMA or PEMA or poly(C.sub.3 -C.sub.24)alkyl methacrylate are not compatible with polystyrene (DE-OS 37 30 025.3).
Certain alkyl-substituted polystyrenes are compatible with certain polyalkyl methacrylates (see DE-OS 36 38 443.7). An example cited in DE-OS 36 38 443.7 is poly-t-butylstyrene and (3,3,5-trimethylcyclohexyl methacrylate). Compatibility of mixtures of polystyrene and poly(meth)acrylic acid esters of substituted heterocycles with 5-8 ring atoms if the heterocycles have at least 2 heteroatoms in the ring has been found (DE-OS 38 18 837.6).
Thus, the art confirms the correctness of the prevailing view of compatible polymer mixtures, namely that incompatibility is the rule and compatibility is the exception, and that the present level of theoretical understanding of the phenomenon of polymer compatibility does not enable reliable prediction.
Mechanical mixtures of polymers (polyblends) have led to plastics products with improved properties in certain areas of the plastics industry (see Kirk-Othmer, 1982, "Encyclopedia of Chemical Technology", 3rd Ed., Vol. 18, pub. John Wiley, pp. 443-478). The physical properties of such polyblends ordinarily represent a compromise, which in general can provide an improvement in the properties over those of the individual polymers.
As a rule, however, it is multiphase polymer mixtures which have achieved commercial importance rather than the few known compatible mixtures (see Kirk-Othmer, loc. cit., pg. 449).
A particularly interesting case of a multiphase polymer mixture is that of mixtures of PVC and/or polystyrene or polycarbonate or SAN, with a graft polymer produced in two steps, comprised of a copolymer of methyl methacrylate in the amount of 10-80 wt. % and an elastomer in the amount of 90-20 wt. %, wherewith the methyl methacrylate copolymer is comprised of units of a cycloalkyl (meth)acrylate in the amount of between 5 and 50 wt. %. All of these mixtures have excellent impact strength (DE-OS 37 43 199.4).
As discussed above, multiphase and compatible polymer mixtures are quite different, in their physical properties and in other properties which have industrial applications, particularly optical properties (transparency, clarity, etc.). Further, the strategy of creating a mixture of plastics to attain an improved overall spectrum of properties is often limited by limits on compatibility. This appeared to be the case for the two polymer classes of polystyrenes and polyalkyl meth)acrylates. (See Kruse, W.A. et al., 1976, Makromol. Chem., 177, 1145; and Somani, R.H., and Shaw, M.T., 1981 Macromolecules, 14, 1549-1554.)